The present invention relates to the field of encoding and decoding digital data from transmission.
U.S. Pat. No. 5,696,790 issued to Graham et al. (the '790 patent) discloses a data transmission method where data is transmitted by two states using a first signal having a first duration to represent one digital state and a second signal having a second duration different than the first duration to represent a second digital state. The '790 patent is hereby incorporated by reference in its entirety.
The '790 patent is directed to a communication system used in a local area network using traditional phone wiring. For example, telephone wiring comprising twisted pair lines are used to connect a central office to various office locations using single wiring connections. The method disclosed in the '790 patent allows computers and/or printers to operate in a network environment independently and transparently to the operation of ordinary telephone service while sharing the same set of twisted pair lines.
One problem facing the transmission method disclosed in the '790 patent is the DC component incurred to the transmission line because of the difference in lengths of the first signals and the second signals. This DC component affects normal operation of the telephone line.
Another problem facing the '790 patent is the possible bandwidth collisions between the bandwidth used in the '790 patent and the bandwidth for the DSL transmission which currently uses the same transmission line. In some instances, the bandwidth used in the transmission method disclosed in the '790 patent overlaps the bandwidth of the DSL transmission and/or regular telephone transmission frequency band. Therefore, it is desirable to have another form of data communication method using the traditional phone wiring while not colliding with the regular telephone signals and the DSL signals.